Method of testing well tubing



April 4, 1950 A. H. BRANDoN v2,502,775

mamon oF TESTING WELL TUBING Filed Aug. 2. 194s Patented Apr. 4, 1950UNITED STATES PATENT OFFICE METHOD F TESTING WELL TUBING Arthur H.Brandon, Los Angeles, Calif. Application August 2, 1948, Serial No.42,054

(Cl. v33-178) 2 Claims. l

This invention relates to a method and. apparatus for testing welltubing and is applicable to various types of tools adapted to be loweredinto wells containing salt water wherein electrical circuits are to beclosed in the well to operate surface indicators.

In practically all oil wells that are deeply drilled, salt water isencountered to a greater or less degree and near the bottom of somewells the water encountered is practically pure salt water and in astate of nearly complete saturation. In the operation of a tubing testerin such wells which may be of the character described in the articleentitled Determining Wall Thickness of Tubing in Wells by Wallace A.Sawdon, appearing in The Petroleum Engineer for July, 1944, when saltwater is encountered by the tubing tester it functions as an excellentconductor across the points of the circuit-closing means so that,although the circuit may not have been mechanically closed by thefingers of the tubing tester, it is nevertheless actually closed by theconductivity of the salt water encountered. Consequently the surfacerecorder or indicator willf falsely indicate defective tubing or thedifference in the reading of the surface indicator when the circuit ismechanically closed over the reading obtained when the circuit ismechanically open but electrically closed by the salt water is so slightthat the locations of the defective tubing are hardly discernible.

It is therefore an object of the present invention to provide animproved method and apparatus whereby readings of this character may beobtained with great accuracy despite the shortcircuiting effect of thesalt water that may be encountered in the well.

More specifically, an object of the invention is to provide an improvedapparatus and method of this character wherein the applied voltage tothecircuit-closing means that is lowered into the well is of a very lowvalue. Heretofore in instruments of this character the applied voltagehas normally been in the neighborhood of approximately two volts but inaccordance with the present invention the applied voltage is reduced toa voltage of between and 30 millivolts. The circuit-closing means thatis lowered into the well has the points thereof usually formed of twounlilze metals, that is, the body of the instrument and thetubing-engaging fingers are usually formed of steel whereas the contactthat is mechanically engaged by the fingers is usually formed of brassor bronze. When the circuitclosing means encounters the salt water inthe well, these unlike metals, being thus immersed in the salt waterelectrolyte, become the poles of a galvanic cell generating a smallamount of electric current. By having the applied voltage and thevoltage developed by this galvanic cell arranged in opposition to eachother, the shortcircuiting effect of the salt water is largely, if notentirely, neutralized so that the surface indicator is not actuated oris only actuated to a minor degree until such time as the circuitclosingmeans mechanically causes the circuit ts be closed. In this manner it ispossible in accordance with the present invention to largely eliminatethe short-circuiting effect of the salt water encountered in oil wellsand to obtain a highly accurate record on the surface indicator of whenthe electrical circuitl is mechanically closed by the instrument loweredinto the well.

vWith the foregoing and other objects in view, which will be mademanifest in the following detailed description and specifically pointedout in the appended claims, reference is had `to the accompanyingdrawings for an illustrative embodiment of the invention wherein:

'I'he figure is a schematic diagram of an apparatus used in accordancewith the present invention.

Referring to the accompanying drawings wherein similar referencecharacters designate similar parts throughout, T indicates the tubing tobe tested as to its wall thickness. The instrument employed for lthispurpose consists of a suitable body generally indicated at lll which haspivotally mounted thereon on pivots il a plurality of fingers l2. Thesefingers have their lower ends urged outwardly such as by springs I3 intoengagement with the interior of the tubing T. The upper ends of thefingers are arranged to traverse the bottom edge of an insulated ring I4which is insulated from the body lll such as by insulation l5. Centeringsprings i6 and il which are also engageable with the interior of thetubing serve to hold the body centrally with relation to the tubing asthe instrument is drawn therethrough. If the tubing T is of normal wallthickness, then the fingers I2 will remain in the full line positionshown wherein the ring I d is not engaged by their upper ends. On theother hand, if a section of tubing of subnormal wall thickness isencountered, one or more of the nngers may expand into the dotted lineposit-ion shown wherein the upper end of any expanded finger will engagethe bottom surface of the insulated ring i4 thus closing the electriccircuit.

The ring I4 is electrically connected to a lowering cable or line I8within which there is an insulated electrical conductor I9.

The applied current is supplied from a battery 20, the terminals ofwhich are connected across a voltage divider or potentiometer indicatedat 2i. This voltage divider in turn is connected to a conductor 22through a millivolt meter 23 to the conductor i9. A conductor 24 leadsfrom one side of the potentiometer 2l to an interrupter 25 which in turnis connected by a conductor 26 to ground or to the tubing T. Theinterrupter in turn is connected to an ampliiier 21 which in turn isconnected through a rectifier 28 and a volt meter 2 to a conventionalpen recorder 30. Across the conductors i8 and 26 there is connected ashort-circuiting switch 3l which is in series with a variable resistance32.

In the use of a tool of this character as performed heretofore, theapplied voltage supplied by the battery 'to directly to the tubingtester has been in the neighborhood of from 2 to 6 volts inasmuch as novoltage divider or potentiometer 2i was employed. When the tubing testerwas lowered into a tubing filled with oil the oil having no greatconductivity would not short circuit between the iingers I2 and the ringlil. Consequently, no record or indication would be made on the penrecorder 3o until such time the fingers l2 encountered tubing ofsubnormal wall thickness. When this occurred one or more fingers I2would be expanded or pivoted on their pivots li so that these fingerswould engage the ring lll closing the electric circuit and causing thepen recorder 3B to be actuated to make a record or an indication of suchtubing.

However, when salt water was encountered the conductivity of the saltwater would short circuit or close the circuit between the fingers I2and the ring It so that even though none of the nngers I2 mightmechanically engage the ring I4 the pen recorder 30 would neverthelessbe actuated.

In accordance with the present invention, inasmuch as the ring I4 isformed of brass and the body of the tool, including the fingers I2, .Isusually formed of steel, the tool on entering the salt water becomes agalvanic cell generating a minor amount of electric current with thetool and its hgers becoming the negative pole of such cell and the ringI4 becoming the positive terminal thereof. Consequently, an electricalpotential would be generated by the tool itself in the directionindicated by the arrow opposite the cable I8, that is, the tool and thetubing T would become the negative while the conductor I9 would bepositively charged. The amount of current generated by this galvaniccell formed by the tool itself is, of course, very small but as theconductor I 9 is connected to the negative side of the millivolt meter23 it is sufficient to cause the needle and the millivolt meter toattempt to swing below zero. To compensate for this the voltage divideror potentiometer '2| is adjusted so that the voltage supplied throughconductor 22 is slightly below the voltage generated by the tool itself.Usually this adjustment is made by closing the short-circuiting switch3| before the tubing tester is lowered into the tubing and adjusting thevariable resistance 32 to substantially equal the resistance of theconductor I9. The short-circuiting switch 3I is then opened and isallowed to remain open after which the tool is lowered into the tubing.Whenever the tool is immersed in oil or other relatively non-conductingmedium, no current will flow until such time il S as one or more of thefingers I2 expand to cause their upper ends to engage the ring I4. Asthe applied current supplied from the battery 20 is direct current, theclosing of the circuit between I2 and I4 causes an interrupted directcurrent to be supplied from the interrupter 25 to the amplier 21. Theinterruptor 25 may be any suitable means for interrupting the directcurrent in the circuit closed by the fingers I2 engaging the ring I4.The interrupted current may. of course, be amplified by the amplifierwhich may be of any conventional construction and after having beenlamplified the current delivered therefrom is rectified by the rectifier28. The use of such rectifier is necessary only because the usual penrecorder 3b is operated by direct current.

When salt water is encountered in the tubing such salt water, instead ofacting as a conductor, short-circuiting between the fingers I2 and thering i4, causes the tool to function as a galvanic cell in opposition tothe current supplied from the battery 2H through the potentiometer 2l.If the voltage supplied by the tool is in excess of the voltage suppliedthrough conductor 22 from the potentiometer, this is observable on themillivolt meter 23 and by adjusting the potentiometer 2I the needle ofthe millivolt meter 23 may be returned to zero when the :lingers i2 areout of engagement with the ring I4. Consequently, even though the toolmay be in salt water, due to the opposition of the two voltages nocurrent is flowing through the circuit to be amplified by the amplifier21. Under these circumstances it is only when the fingers I2mechanically close the circuit by engaging the ring I4 when the fingershave encountered tubing of subnormal wall thickness that current willflow through the circuit, be interrupted by the interrupter 25, ampliedby the amplifier -21, rectied through the ectiiler 28, and used toactuate the pen recorder From the above described construction it willbe appreciated that an improved method and apparatus has been developedfor actuating a surface indicator or recorder by a circuit-closing meanswhich is adapted to be lowered into a well and encounter salt Watertherein. The short-circuiting effect of the salt water across thecontacts of the circuit-closing means while in open circuit position iseiectively neutralized by causing the tool itself to be so constructedthat when immersed in salt water it becomes a galvanic cell so arrangedthat the Voltage generated thereby will be opposed to the suppliedvoltage. It is, of course, possible to accomplish nearly the same effectbut with a greater potential by attaching a piece of zinc to the bodyIII which is insulated therefrom and electrically connected to theconductor I9. This zinc, together with the steel of the body, wouldlikewise form a. galvanic cell functioning in the same manner. In theusual situation, however, as the ring I4 is already formed of brass orbronze, the use of such additional zinc is unnecessary.

Various changes may be made in the details of construction withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

I claim:

1. The method of testing in wells comprising introducing into the tubinga circuit closing means operable to close an electric circuit whendefective tubing is encountered, said circuit closing means beingcharacterized by being effective to generate an electromotive force whenimmersed in salt water, applying to the contacts of the circuit closingmeans a voltage in opposition to the electromotive torce generated bythe circuit closing means, the applied voltage being o! a magnitudesubstantially equal to that generated by the circuit closing means sothat substantially no current flows through the electric circuit, movingthe tester through the well into a salt water zone and onward untildefective tubing is encountered to close the circuit thereby stoppingthe galvanic eiiect, and measuring the current flowing in the electriccircuit during the testing operations.

2. The method of testing in wells comprising introducing into the tubinga circuit closing means operable to close an electric circuit whendefective tubing is encountered, said circuit closing means beingcharacterized by being etfective to generate an electromotive force whenimmersed in salt water. applying to the contacts of the circuit closingmeans a voltage in opposition to the electromotive force generated bythe circuit closing means. the applied voltage being of a magnitudesubstantially equal to that gen- ARTHUR H. BRANDON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,322,343 Brandon June 22, 19432,392,357 Bays Jan. 8, 1946 2,397,255 Ennis Mar. 26, 1946 2,415,636Johnson Feb. 11, 1947 2,427,950 Doll Sept. 23, 1947

